The production of nickel, cobalt and other metal powders by pressurized hydrogen reduction of aqueous ammoniacal sulfate solutions is a commercial practice pioneered by Sherritt Gordon Mines in Canada. In the process, it has been found that reduction kinetics are improved by the presence of particulate seed material such as fine nickel or cobalt powder. Such powders may come from many sources and may be introduced into the autoclave to act as nuclei for powder formation. U.S. Pat. No. 2,796,343 mentions the production of fine metal particles for use as seed by operations such as grinding of larger particles; precipitation by such reducing agents as hypophosphite, hydrazine and the like which are stronger than hydrogen, decomposition of nickel carbonyl and the limited reduction of acidic solutions. U.S. Pat. Nos. 2,734,821, 2,796,342 and 2,796,343 describe "self-nucleating" solutions in which agents such as stannous, cerous, manganous, ferrous, titanous, vanadous and chromous salts are added.
Known cobalt and nickel powders produced by the hydrogen reduction method are usually coarse, spherical powders since the usual practice is to repeatedly precipitate further metal upon the initially formed particles by further "densifications".
There are needs in the art for ultrafine powders.
Production of nickel, iron and cobalt powders by reduction of the metal ion or ions with reducing agents such as borohydrides, hypophosphates, borane, borazane, etc. is also known from patents such as U.S. Pat. Nos. 3,669,643 and 4,096,316. Such powders are said to be useful for magnetic applications.
The invention is directed to the production of fine nickel powder by hydrogen reduction at elevated pressure.